Electric arc furnace side-wall protection arrangement

ABSTRACT

An electric arc furnace has a side wall lining with at least one portion bombarded by the arc flare from one of the furnace arcing electrodes. A magnet is positioned on the outside of this portion and ferro-magnetic particles are fed to its inside, the magnet forming a magnetic flux field traveling through this lining portion and on the latter&#39;&#39;s inside magnetically holding the particles to form an arc flare shield protecting this portion&#39;&#39;s inside from the arc flare. As the particles heat to their Curie point temperatures, they become non-magnetic and fall into the melt of the furnace, a supply of fresh and relatively cold particles being fed to the flux field as required to maintain the efectiveness of the arc flare shield formed by the particles. The wall thickness of this portion is reduced from its outside inwardly to form a recess in its outside and in which the magnet is positioned to reduce the distance the flux field must travel to the inside to hold the ferro-magnetic particles. Between the magnet and this thin wall portion a water cooled plate is positioned to cool the thin wall portion of the lining. In this way the travel path of the magnetic flux is reduced in length without risking possible overheating of the lining, permitting the use of a less powerful magnet construction, this being an electromagnet and requiring electric solenoids, a core or cores with pole pieces and a suitable mounting arrangement. A temperature measurement sensor is installed in the thin wall of the lining portion protected by the flare shield, and equipment is provided for controlling the feed rate of the ferro-magnetic particles which form the shield, automatically in response to the temperature measurements obtained from this sensor, this assuring maintenance of the effectiveness of the shield. The water-cooled plate internally has magnetic pole piece extensions for the pole pieces for the electromagnet core or cores and which form magnetic paths for the flux which must travel through the watercooled box.

United States Patent [1 1 Hanas Primary ExaminerG. Harris Attorney,Agent, or Firml(enyon & Kenyon Reilly Carr & Chapin [5 7] ABSTRACT Anelectric arc furnace has a side wall lining with at least one portionbombarded by the arc flare from one of the furnace arcing electrodes. Amagnet is posimagnetic particles are fed to its inside, the magnetforming a magnetic flux field traveling through this [H1 3,885,082 [4 1May 20, 1975 lining portion and on the latter's inside magneticallyholding the particles to form an arc flare shield protecting thisportions inside from the arc flare. As the particles heat to their Curiepoint temperatures, they become non-magnetic and fall into the melt ofthe furnace, a supply of fresh and relatively cold particles being fedto the flux field as required to maintain the efectiveness of the arcflare shield formed by the particles. The wall thickness of this portionis reduced from its outside inwardly to form a recess in its outside andin which the magnet is positioned to reduce the distance the flux fieldmust travel to the inside to hold duced in length without riskingpossible overheating of the lining, permitting the use of a lesspowerful magwall of the lining portion protected by the flare shield,and equipment is provided for controlling the feed maintenance of theeffectiveness of the shield. The water-cooled plate internally hasmagnetic pole piece extensions for the pole pieces for the electromagnetcore or cores and which form magnetic pathgg -tbr the flux which musttravel through the water-cooled box.

6 Claims, 3 Drawing Figures ELECTRIC ARC FURNACE SIDE-WALL PROTECTIONARRANGEMENT BACKGROUND OF THE INVENTION An electric arc furnaceconventionally comprises a shell containing a non-metallic refractorylining, and it has a cover or roof through which electrodes pass withlower ends reaching down to form arcs between the lower arcing ends ofthe electrodes and a metal melt in the bottom or hearth portion of thelining. Although other electrode arrangements are possible, when thefurnace is powered by three-phase alternating current, there are threeelectrodes usually arranged in triangular formation. This positions theelectrodes close enough to the furnace side wall lining above the melt,so that the adjacent portions of the lining are bombarded by the arcflares. These flares are in the form of both radiation and particleswhich bombard the portions of the side wall lining adjacent to the arcs.If the electrodes are positioned to form a straight line of electrodes,it is the flares from the end electrodes which bombard the adjacentportions of the side wall lining.

Any portion of the side wall lining bombarded by an arc flare, issubjected to more heat and more rapid erosion and wear than the balanceof the lining. It is, of course, undesirable to have portions of thelining rendered unserviceable prior to the balance of the lining.

One proposal to protect such bombarded portions of an electric arcfurnace side wall lining, is disclosed by the Daniel J. Goodman U.S.Pat. No. 3,619,467, dated Nov. 9, 1971, the disclosure of which ishereby incorporated into the present disclosure, by this reference tothat patent. The Abstract of that patent is quoted below:

Damage to the lining of the shell of an electric arc furnace by areflare during steel making is reduced by providing a powerful magneticfield in the vicinity of the lining sidewall area subjected to theintensive heat from the arc flare and then feeding pieces, pellets orfragments of magnetically attracted ferrous material, such as iron oreor metal pieces, pellets or fragments past the magnetized lining area tothe mo]- ten metal and slag bath in the bottom or hearth of the furnace.This magnetic flux causes the falling fragments, such as concentratediron ore pellets, to be captured by and to adhere temporarily to thelining of the furnace until their temperatures reach the socalled Curiepoint of about 700C. at which their capability of being magneticallyattracted ceases. Thereupon the pellets fall into the molten bath butare immediately replaced by fresh pellets falling past the magnetizedwall and thus providing a continuous shield of pellets or othermagnetizable fragments which provide substantial protection to thesidewalls or lining of the furnace. The portions of the furnace betweenthe electromagnets providing the magnetic flux and the furnace lining atthe locations subjected to damaging arc flare are preferably formed ofnonmagnetic material, so as to maintain the magnetic flux flow throughthe furnace wall and lining at its maximum value."

In the above proposal, the magnetic flux produced by the electromagnetsmust travel through the thick nonmetallic refractory side wall liningbefore forming the flux field useful for holding the magnet particlesforming the flare shield. This makes it necessary to use undesirablylarge electromagnet assemblies and, of course, requires an undesirablyhigh consumption of current. Even so, as indicated by the patent, themagnetic particles must be in the form of pellets or fragments, such asconcentrated iron ore pellets. It has been considered that concentrateiron ore in powdered form cannot be used satisfactorily.

Another prior art approach to protecting the bombarded portions of thefurnace side wall lining, has been to apply water cooled plates to theoutside of the metal furnace shell which conventionally contains thefurnace lining, the object being to in this way remove heat from theaffected lining portions more rapidly through the lining and the metalshell. An example of this is shown by Swedish patent specification328,599. However, with large electric arc furnaces using powerful arcs,the improvement effected leaves further improvement desirable.

SUMMARY OF THE INVENTION The present invention may be regarded as animprovement on the patented proposal using the electromagnets on theoutside of the furnace side wall lining, at the bombarded portions, inconjunction with the feed of ferro-magnetic particles into the fluxfields thus created on the insides bombarded by the arc flares.

This improvement comprises the formation of a recess in the outersurface of each affected furnace side wall lining portion, so that thisportion has a reduced wall thickness as compared to the balance of thelining. In this way the travel path of the flux through the lining isreduced in extent, permitting the use of smaller electromagnetstructures to provide a flux field on the inside for holding themagnetic particles effectively and, of course, a reduction in theelectric power consumption that was previously required. To protect thiswall portion of reduced thickness against the possible risk ofoverheating, a water-cooled plate is interposed between theelectromagnetic structure and this wall portion and in contact with thelatter's inside. The thickness of this plate need not be very great,permitting the electromagnet structure pole piece to be positionedinside of the recess and thus substantially closer to the inside of thebombarded lining portion.

To further protect the bombarded side wall portion from overheating, atemperature sensor is built into this portion and connected to a feedrate controller for the feed of ferro-magnetic particles. This is donein such a way as to make the feed rate of the particles into themagnetic field on the inside of the furnace lining side wall, increaseas the temperature of the thinned wall portion increases, and todecrease when the tempera.- ture drops below a value indicating that thewall portion is at lower temperatures. As the ferro-magnetic particlesare heated to their Curie points, become nonmagnetic and fall, new freshparticles of lower temperatures are thus fed as replacements. With thethickness, and therefore protective effectiveness, of the flare shieldmaintained at a substantially constant value, the portion of reducedwall thickness can be relied on to have a service life substantially aslong, if not as long, as the balance of the furnace lining.

With this invention the magnetic flux path length through the lining canbe very substantially shortened, and with an electromagnetic structureor assembly of the size and power as formerly required, a very intensiveflux field of great force may be maintained on the inside of the liningwhere the protection is needed against the arc flare. This makes itpossible to use a feed of powdered concentrated iron ore for thecreation and maintenance of the arc flare shielding, althoughconcentrated iron ore in the form of pellets or fragments of substantialsize, as well as ferro-magnetic metal pieces, such as steel scrapparticles, may be used,

but such use is not to be considered mandatory as it was before.

The water-cooled plate must have a certain thickness to be effective incooling the inside of the side wall portion with which it contacts. Tothis extent the flux path between the electromagnet pole piece ends, orthe ends of its solenoid cores, cannot be positioned so that the fluxtravel path or paths must be only as long as the thinned wall portion isthick. Therefore, according to the present invention, the water-cooledplate or box, whether or not it has outer walls made of non-magneticmetal, is internally provided with magnetic pole piece extensionsextending from its outer wall which may be substantially in contact withthe electromagnets pole pieces, transversely with respect to the plateand to the plate s inner wall, which is in contact with the outside ofthe portion of the furnaces side wall lining which is reduced inthickness. Customarily, a water-cooled plate is internally provided withtransverse baffle walls for the purpose of controlling the flow ofinternal cooling water as required to obtain the maximum cooling actionpossible. Such baffle or internal walls, particularly if thickened andmade of magnetic metal, may form the pole piece extensions internallywithin the plate, providing the baffles or walls are co-extensive withthe front and back walls of the plate and form integral extensions forthe magnetic circuit. With this invention, the entire water-cooled platemay be made of magnetic metal, if desired. However, if the cooling plateouter walls are made of non-magnetic metal and the magnetic metalbaffles which function to carry the flux between these walls arearranged in separate groupings, the effect of two or more distinctlyseparated pole piece extensions may be provided for two or more polepieces of an electromagnet on the outside of the cooling plate.

BRIEF DESCRIPTION OF THE DRAWINGS The presently preferred mode ofcarrying out the invention is schematically illustrated by theaccompanying drawings, in which:

FIG. 1 is a vertical section of an electric arc furnace to which theinvention is applied;

FIG. 2 is a vertical section through one of the watercooled plates, thisview being partly in perspective; and

FIG. 3 is a vertical section through a prior art watercooled plate.

DETAILED DESCRIPTION OF THE INVENTION Referring to the above drawing,the furnace vessel is indicated as having a lower portion or hearth land a side wall 2 which extends upwardly from this portion 1, aremovable cover 3 covering the top of the vessel. Although not shownbecause of its familiarity in the prior art, the furnace vessel normallyhas a steel shell on its outside with the portions 1 and 2 formed by anonmetallic, refractory lining, only this lining being shown by thedrawing. Cantilever arm 4 mounts the electrodes 11 which are suspendedthrough openings in the cover 3. Although shown for only one of theelectrodes, each of the electrodes forms an are 110, the extremely hotlower end portion of the electrode producing the arc flare 12 consistingof thermal radiation and possibly particles, the intensity of thebombardment action depending on the power applied to form the are 110.The arcs are, of course, between the bottom ends of the electrodes andthe metal melt 13 in the lower or hearth portion 1 of the vessel. Thebombarded portion of the side wall, of which there are more than one, isindicated at 14 as being formed by refractory bricks from which theentire side wall lining 2 may also be formed. The inside surface of thisportion 14 is flush with the generally cylindrical plane of the insideof the furnace side wall lining 2.

However, on the outside of this bombarded portion, the furnace lining isformed with a recess 14a so that this portion 14 has a reduced wallthickness. As indicated by the drawing, this reduced wall thickness isvery substantially thinner than the balance of the side wall lining 2.For its protection against possible overheating, its inside is incontact with hollow watercooled cooling plate or box 15. A continuouscirculation of cooling water is maintained in this plate or box 15 asindicated by the arrows A-A. For illustrative reasons, this plate or box15 is shown as being possibly somewhat thicker than should be used; theplate or box 15 takes up as little space in the horizontal direction asis possible, consistent with adequate cooling of the thinned wallportion 14.

The recess 14a and the relative thinness of the side wall portion 14 andof the plate or box 15, permit the pole pieces 16 and 17 of anelectromagnet assembly, to

be positioned in the recess to provide the shortened flux travelpreviously described. These pole pieces are shown as provided by a corewith which an electrically powered solenoid 8 is associated. Prior artknowledge of electromagnet design may be used, but the pole piece endswhich create the flux field should be positioned inside of the recess14a, with the flux path travel distance shortened as much as possible.The furnaces steel shell should have openings or cutouts to provide thenecessary clearance for the recess 14a, and for installation of thewater-cooled plate 15, and insertion of the pole piece ends, if not themajor part of the electromagnet assembly, in the recess 14a.

The feed for the ferro-magnetic particles which in the case of thisinvention may be powdered concentrate iron ore as well as iron orepellets or fragments, is through a suitable feeder 18 in the furnacecover 3. There may be a plurality of these feeders, or feeders in theform of circular segments may be used. The feed of the material is underthe control of a feed controller 19 which may be an electricallycontrollable valve. With the controllable valve or feed controller, thetemperature sensor is shown at 20 as controlling this valve orcontroller 19 via a proportional or proportional integrating type ofamplifier 21. The sensor 20 may be of the type disclosed by the Otto vonKrusenstierna et al U.S. Pat. No. 3,512,413, dated May 19, 1970. Thecontrol circuitry is such that the feed through the feeder 18 increasesif the wall temperature of the portion 14 increases, with the feed ofparticles decreasing if the wall temperature at 14 decreases. In thisway the supply of ferro-magnetic particles, required to replaceparticles heated above their Curie points and falling, is madeautomatically responsive to the wall temperature of the portion 14,assuring the maintenance of an arc flare shield adequate to protect thethinned portion 14 against overheating; this protection is in additionto that afforded by the cooling plate or box 15. If powdered iron oreconcentrate is used, this feed, via the feeder or duct 18, may bereinforced by a stream of carrier gas of suitable composition and underthe pressure of a compressor or blower (not shown), in which case,assuming the compressor or blower is powered by an electric motor, themotor speed may be varied under the control of the sensor 20.

Because of the possibility of providing a very strong flux field in theinside of the wall portion 14, a relatively high speed stream of theferro-rnagnetic particles in powdered fonn, for example, can be used toadvantage. The magnetic adhesive force drawing the particles against thewall portion 14 in its inside, may be made very intense.

The foregoing reference to Curie points is to be understood as meaningthat for the composition of the ferro-magnetic material used, thisreference is intended to mean the temperature or temperatures wherethere is change from a magnetic phase to a non-magnetic phase. Underpractical furnace operating conditions, the points can be detectedbecause the particles will fall into the melt and require replacement.It is well known that the length of the path through which magnetic fluxmust travel determines the intensity or strength of the flux field atthe location where this field is to do useful work, which in the presentinstance is the attraction and holding of the ferro-magnetic particles.

In accordance with the present invention, the watercooled plate or box15 is shown as having the magnetic metal baffles or walls arranged astwo groups, 22 and 23, the group 22 being aligned with the pole piece 16and the group 23 being aligned with the pole piece 17. These baffles 22extend transversely between the front and back walls of the plate 15continuously and without gaps and may be made thicker than shown by theschematic drawings of this application. Being in two groups, the bafflesform two distinct pole piece extensions for the pole pieces 16 and 17,to establish a typical flux field indicated at F by the curved arrows.With the baffles or walls, forming these pole piece extensions, madethick enough, the effect is close to that of the pole pieces 16 and 17being in contact with the inside of the wall portion 14 of reducedthickness. By making the outer walls of this water-cooled plate ofnon-magnetic metal, the effect of a magnetic short circuit can beavoided, the gap being between the ends of the baffles 22-23 towards thefurnace interior.

As indicated, the baffles 22 must be in effect continuous magnetic pathsextending from the magnet pole pieces to the inside of the wall portion14. FIG. 3 shows the conventional baffle arrangement for a coolingplate, the baffles 24 in this instance failing to reach from the frontto the back side walls of the plate. Any such arrangement would forminterruptions from the magnetic travel path. As shown in FIG. 2, withthe present invention with the continuous baffles 22 and 23, the bafilesmay at judicious points be formed with holes 25 effecting the necessaryintercommunication between the baffles where required. These holes willhave some effect on the continuity of the magnetic path, but this effectwill be minimal. It would also be possible to provide externalmanifolding of the ends of the channels defined by the continuousbaffles of the present invention.

What is claimed is:

1. An electric arc furnace comprising at least one electrode having anend forming an are producing an arc flare, a side wall lining having atleast one portion having an inside positioned to be bombarded by saidflare, said portion having an outside, a magnet having pole-piece endson said outside forming a magnet flux field traveling through saidportion and beyond said inside and on said inside holding ferro-magneticparticles forming a flare shield until the particles are heated to theirCurie point temperatutes, and a feeder for feeding said field withreplacement ferro-magnetic particles at temperatures lower than theirCurie point temperatures; wherein the improvement comprises said lininghaving an outer surface in which a recess is formed at said portion sothat said portion has a reduced wall thickness through which said fluxfield must travel, and means between said magnet and recess forwatercooling said portion of reduced wall thickness, said water-coolingmeans including magnetic pole piece extensions extending substantiallyfrom said pole piece ends to said inside of said portion.

2. The furnace of claim 1 in which said flare shield is formed by ironore particles in powder form.

3. The furnace of claim 1 in which said magnet pole piece ends areinside of said recess.

4. The furnace of claim 3 in which said means is a water-cooled platepositioned against said outside be tween the latter and said magnet polepiece ends, said plate having interspaced inner and outer side walls,said inner wall being substantially in contact with the inside of saidportion and said outer wall being at least adjacent to said pole pieceends, and between said inner and outer walls said plate havingcontinuously extending therebetween magnetic metal pole piece extensionsfor said pole piece ends.

5. The furnace of claim 4 in which said feeder has a feed ratecontroller and means for actuating said controller automatically inresponse to the temperature of said portions.

6. The furnace of claim 4 in which said extensions comprise baffles fordistributing cooling water in said plate.

1. An electric arc furnace comprising at least one electrode having anend forMing an arc producing an arc flare, a side wall lining having atleast one portion having an inside positioned to be bombarded by saidflare, said portion having an outside, a magnet having pole-piece endson said outside forming a magnet flux field traveling through saidportion and beyond said inside and on said inside holding ferro-magneticparticles forming a flare shield until the particles are heated to theirCurie point temperatutes, and a feeder for feeding said field withreplacement ferro-magnetic particles at temperatures lower than theirCurie point temperatures; wherein the improvement comprises said lininghaving an outer surface in which a recess is formed at said portion sothat said portion has a reduced wall thickness through which said fluxfield must travel, and means between said magnet and recess forwater-cooling said portion of reduced wall thickness, said water-coolingmeans including magnetic pole piece extensions extending substantiallyfrom said pole piece ends to said inside of said portion.
 2. The furnaceof claim 1 in which said flare shield is formed by iron ore particles inpowder form.
 3. The furnace of claim 1 in which said magnet pole pieceends are inside of said recess.
 4. The furnace of claim 3 in which saidmeans is a water-cooled plate positioned against said outside betweenthe latter and said magnet pole piece ends, said plate havinginterspaced inner and outer side walls, said inner wall beingsubstantially in contact with the inside of said portion and said outerwall being at least adjacent to said pole piece ends, and between saidinner and outer walls said plate having continuously extendingtherebetween magnetic metal pole piece extensions for said pole pieceends.
 5. The furnace of claim 4 in which said feeder has a feed ratecontroller and means for actuating said controller automatically inresponse to the temperature of said portions.
 6. The furnace of claim 4in which said extensions comprise baffles for distributing cooling waterin said plate.